1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus including a recording head for ejecting liquid droplets and a head tank for supplying liquid to the recording head.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid ejection head or liquid-droplet ejection head) for ejecting droplets of ink or other liquid.
To replenish and supply liquid from a main tank to a head tank (also referred to as “sub tank”) mounted on the recording head even during printing operation, such an image forming apparatus may have a displacement member (hereinafter also referred to as “feeler”) mounted on the head tank and displaceable with the remaining amount of liquid in the head tank, a first sensor mounted on a carriage to detect that the displacement member is at a predetermined first position, and a second sensor mounted on an apparatus body to detect that the displacement member is at a predetermined second position. The image forming apparatus detects and retains a differential supply amount corresponding to a displacement amount of the displacement member between the first position and the second position. In supplying liquid from the main tank to the head tank without using the second sensor on the apparatus body, the image forming apparatus supplies liquid to the head tank by the differential supply amount after detection of the displacement member with the first sensor (see JP-2011-207206-A).
For the configuration described in JP-2011-207206-A, in a case in which the displacement member is between the first position detected with the first detector and a supply start position (referred to as “third position”) while the image forming apparatus is halted or turned off for a long time after printing operation, the position of the displacement member may change due to changes in the ambient environment or permeability of a liquid supply passage including the head tank. As a result, when the next printing operation starts, the actual position of the displacement member may differ from an assumed position of the displacement member corresponding to the consumption amount of liquid at the end of the previous printing operation.
If the next printing operation is performed from the actual position differing from the assumed position until the third position is detected, an excessive negative pressure in the head tank may cause degraded print quality or air sucked into nozzles may cause ejection failure. In addition, when the displacement member is at a position at which the remaining amount of liquid in the head tank is greater than when the displacement member is at the first position, an excessive amount of liquid may be supplied, thus causing liquid leakage from nozzles.